1. Field of the Invention
This invention relates to an electronic control fuel injection device for an internal combustion engine.
2. Discussion of Background
In a conventional electronic control type internal combustion engine, fuel injection quantity is measured by an output signal of an air-flow meter and an engine revolution number. However, in case of the air-flow meter, the intake air quantity can not accurately be measured, since the air-flow meter suffers influence of intake air pulsation when a throttle valve is fully open. Furthermore when a supercharger is installed in the engine, the range for measuring the intake air quantity becomes too wide for the air-flow meter to accurately measure the intake air quantity, over the whole range of the measurement. Therefore the measurement accuracy of the air-flow meter of the intake air quantity in its low flow quantity region and its high flow quantity region, has to be lowered. As a result, when a supercharger is installed in the engine, it becomes difficult to make an air fuel ratio of a mixture to be supplied to a cylinder of the engine, agree accurately to a predetermined air fuel ratio, in the low flow quantity region and the high flow quantity region. Even when the supercharger is not installed of the engine, it is difficult to make the air fuel ratio of a mixture to be supplied to the cylinder of the engine, agree to a predetermined air fuel ratio, when the throttle valve is fully open.
To solve the above problem, in Japanese Unexamined Patent Publication No. 221433/1984, an inner cylinder pressure sensor is introduced, which directly detects a pressure in the cylinder. The air fuel ratio control is performed by calculating the fuel injection quantity which is injected from a fuel injection valve, based on the output of this inner cylinder pressure sensor.
FIG. 1 shows the composition of such conventional device. A reference numeral 1 designates an engine, 2, a piston, 3, a combustion chamber, 4, an intake air valve, 5, an intake air port, 6, a surge tank, 7, a branch pipe which connects the intake air ports 5 of respective cylinders, and the surge tank 6, 8, an intake air duct, 9, a throttle valve installed in the intake air duct 8, 10, an air cleaner, 11, a water temperature sensor which detects a temperature of cooling water of the engine, and 12, a fuel injection valve installed at the branch pipe 7. Fuel is injected from the fuel injection valve 12 to the corresponding intake port. The inner pressure sensor 13 is installed in the combustion chamber 3, which detects an inner cylinder pressure. The electronic control unit 20 is composed of a digital computer, which has the CPU (microprocessor) 22, the ROM 23, RAM 24, the input port 25, and the output port 26, which are interconnected by the bi-directional bus 21. The water temperature sensor 11 generates an output voltage which is proportional to the temperature the cooling water of the engine. This output voltage is inputted to the input port 25, after it is converted to a corresponding binary signal by the AD convertor 27. The inner cylinder pressure sensor 13 generates an output voltage which is proportional to the pressure in the combustion chamber 3. The output voltage is inputted to the input port 25, after it is converted to a binary number by the AD convertor 28. The crank angle sensor 29 generates an output pulse signal at every 1 degree of crank angle. This output signal is inputted to the input port 25. The crank reference position sensor 30 generates the reference position pulse signal at the timing when the intake air valve 4 is closed and a predetermined crank angle elapses. Accordingly, this reference position of signal is generated at every 720.degree. of the crank angle. This reference position signal is inputted to the input port 25. The output port 26 is connected to the fuel injection valve 12 of the respective cylinder, via the drive circuits 31 through 34. Fuel is injected from the fuel injection valve 12, at every 720.degree. in crank angle, at the timing respective to each cylinder.
Next, explanation will be given to the operation. The pressure in the combustion changer 3, is detected by the inner cylinder pressure sensor 13. The fuel injection quantity is controlled by an output signal of the cylinder pressure sensor 13. When the fuel injection quantity is determined based on the pressure in the combustion changer 3 as stated above, irrespective of the running condition of the engine, the mixture having a predetermined air fuel ratio, can always be supplied to the combustion chamber 3. Next, explanation will be given to the reason referring to FIGS. 2 and 3. FIG. 2 shows the pressure change in the combustion chamber 3 from the compression stroke to the expansion stroke, when the intake air quantity (g) is maintained constant. The bold line shows the pressure change in firing time, and the dotted line shows the pressure change in motoring time. FIG. 2 shows that the pressure change in the firing time and that in motoring time are the same until the crank angle reach the points C. The crank angle C is about 40.degree. before the upper dead center. On the other hand, FIG. 3 shows the relationship between the inner cylinder pressure P in the combustion chamber 3 at crank angle C, and the intake air quantity G.sub.a (g). This relationship is shown by a linear equation. This relationship is obtained in the motoring time. When the intake air quantity G.sub.a is constant, the pressure P in motoring time and that in firing time are the same at crank angle C. Therefore the relationship in FIG. 3 is established also in firing time. Therefore, when the pressure in the combustion chamber 3 is measured at the predetermined crank angle C, the intake air quantity G.sub.a which is actually sucked in the combustion chamber 3, can be known. Accordingly, when the fuel injection quantity is determined based on the pressure in the combustion chamber 3, the fuel being proportional to the intake air quantity G.sub.a, can be supplied.
In case of the conventional device composed as above, when the engine revolution number is changed, the proportional relationship in FIG. 3 is changed. Therefore the intake air quantity can not accurately be detected. Furthermore, the inner cylinder pressure may vibrate, by which the intake air quantity can not accurately be detected. Since the timing in which the fuel quantity calculated based on the detected intake air quantity, is injected, is at the next cycle, there is a possibility of always containing an error. The above problems cause the lowering of engine performance, such as an increase of an output torque variation, the lowering of the output torque, the worsening of the fuel consumption ratio, and the increase of HC, or CO component in the exhaust gas, etc.